There have been prior attempts to improve the manufacturability of dental hand pieces. For example, Great Britain publication GB 2 209 284 A to Hiroshi Kimura describes a dental hand piece made of synthetic resin that is integrally molded as one piece. A detachable head piece snap-fits onto the distal end of the hand piece, which is hollow and thin-walled to accommodate the extension therethrough of two fluid conduits in the form of tubes described as being captured during the resin casting process (see page 7, first partial paragraph, last sentence). The reference does not explain precisely how the hand piece is molded, and there is no suggestion of investment casting, and the insertion of tubes in the interior instead the formation of conduits therein is contrary to such a suggestion.
U.S. Pat. No. 4,842,516 to Choisser teaches a disposable prophylactic hand tool having a right-angled head for cleaning, polishing etc. It is preferably made of plastic that presumably is not autoclavable (see column 1, lines 25 through 39 re prior art hygiene problems). A plastic turbine drive mechanism is also described as disposable. A bearing between the plastic endwall and the turbine is said to reduce frictional wear. (See column 3, lines 51 through 59.)
U.S. Pat. No. 5,308,242 to McLaughlin, et al. teaches a disposable hand piece for high-speed drilling, etc. in a two-piece, clamshell arrangement whereby two opposing axial halves are joined along two axial seams (see FIGS. 3A, 3B), but in which the air and/or fluid conduits are integrally molded into either shell half by conventional injection molding (see column 2, lines 39 through 54). The Oralsafe Co. of Temecula, Calif. attempted to make such a disposable, so-called "high-impact" plastic hand piece for use in a high-speed drilling dental application, and, because of the clamshell construction of its hand piece, failed to produce a product that could be repeatably manufactured in such manner as to enable reliable, long-term, high-speed drilling and its attendant fluid pressure and ultra-high-frequency vibration.
U.S. Pat. No. 5,374,189 to Mendoza teaches an integrally formed, preferably plastic, "prophy", i.e. prophylactic, dental hand piece intended for single use and disposal. The reference teaches away from autoclaving as too costly (see column 1, lines 52 through 64).
U.S. Pat. No. 4,648,838 to Schlachter teaches the inclusion in an integrally molded dental hand piece of a light-emitting element axially aligned and directed with the fluid, e.g. air, water, conduits, which assume the form of hoses or thin tubes extending through a large interior hollow of the hand piece (column 3, line 49 through column 4, line 68).
Prior art attempts to manufacture a durable high-speed dental appliance out of injection molded polymeric material has required seams in critical regions that are incapable of withstanding the stresses to which normal use and maintenance put the dental appliance. For example, one prior art approach is the two-piece clamshell arrangement in which essentially mirror-image elongate half-shells are adhered along opposing elongate seams, which seams have been found to fail under the stress of normal use and maintenance. Another prior art approach is the two-piece handle/head configuration in which a seam extends around the hand piece in a plane normal to the hand piece's long axis between separately molded handle and head, which seam also has been found to fail under the stress of normal use and maintenance. Yet another prior art approach is injection or so-called `blow` molding of a hand piece having a single elongate passage therethrough defined by thin sidewalls wherein various conduits in the form of discrete tubes are used for driving the turbine, thereby greatly increasing component count, cost and attendance interconnection difficulties and reliability problems.
Even the traditional machined-metal dental drills are typically of at least two-piece construction. None of the prior art teaches an auto-clavable, unitary construction for such a dental appliance.